The invention relates to a device centered on a predetermined longitudinal axis designed to transmit forces between a central region and end regions of the said device.
The invention is also applicable to a mechanism comprising such a device associated with a cylindrical rod acting as a pivot pin, and forces are transferred between the pivot pin and two parts, one of the parts applies forces to the pivot pin and the pivot pin applies forces to the other part.
The invention also relates to application of a mechanism of this type to the transmission of forces between a linear actuator mounted on a fixed aircraft structure and a control surface that can pivot about the fixed structure, around an axis of rotation parallel to the longitudinal axis of the force transmission part and offset from this axis. In particular, the fixed structure may be an element of a wing, vertical stabilizer, tail fins or the fuselage of the aircraft.
An aircraft control surface is normally articulated on the structural elements of the aircraft, considered as being the fixed part for the mobile control surface so that it can pivot about an axis of rotation related to this fixed part. The rotation movement of the control surface is controlled by a servocontrol materialized by a linear actuator supported on the fixed part of the aircraft. The linear actuator is fitted with a ball end. This acts on the control surface through fittings fixed to the control surface through screws, rivets, etc. The fittings also control rotation of the control surface with respect to the fixed part of the aircraft.
A fitting illustrating the state of the art is diagrammatically shown in perspective view in FIG. 1 on the attached drawings.
In its central region, the fitting generally comprises a double eye plate 1 retaining a first pivot pin (not shown) on which the linear actuator ball end is mounted. In its two end regions, the fitting also comprises a single eye plate 2 through which a second pivot pin (not shown) passes supported by the fixed part. This second pivot pin materializes the Xxe2x80x94X axis of rotation of the control surface. The Yxe2x80x94Y longitudinal axis of the first pivot pin and the Xxe2x80x94X axis of rotation of the control surface are parallel and offset from each other by a distance d. Bearings and rings (not shown) are provided between the double and single eye plates 1 and 2 of the fitting and the pivot pins.
In this known layout, the central point A of the double eye plate 1 of the fitting is at a distance D from the point B half way between each of the single eye plates 2 of the fitting, in a direction parallel to Xxe2x80x94X and Yxe2x80x94Y axes of the pivot pins. The distance d between these axes represents the lever arm of the force transmission mechanism materialized by the fitting. The force exerted by the linear actuator associated with the lever arm generates a rotation moment of the control surface around its Xxe2x80x94X axis of rotation. Thus this controls rotation of the control surface about this axis.
When the control surface is actuated, a large proportion of the forces exerted by the linear actuator pass through the double eye plate 1 located in the central part of the fitting to the single eye plates 2 located at the end part of the fitting through the structures of the fitting or the control surface. The stresses and deformed shapes generated by application of these forces on the structure of the fitting are proportional to the distance D between the double eye plate 1 and each of the single eye plates 2 in the fitting, in a direction parallel to the Xxe2x80x94X and Yxe2x80x94Y axes of the pivot pins.
In practice, the distance between the single eye plates 2 placed at the ends of the fitting and consequently the distance D, depend on the size of the actuator and the clearances necessary for maintenance operations. Furthermore, the size of the actuator depends on its type (EHAxe2x80x94xe2x80x9cElectro-Hydraulic Actuatorxe2x80x9dxe2x80x94, EBHAxe2x80x94xe2x80x9cElectro-Backup Hydraulic Actuatorxe2x80x9d, etc.), its characteristics (stop load, distance traveled, etc.) and the technology used (hydraulic unit made of aluminum, titanium, etc.).
Therefore when the size of the servocontrol increases, the distance D between the double eye plate 1 connected to the central part of the fitting and the single eye plates 2 located at the ends of the fitting has to be increased. This results in a large increase in the mass of the fitting to limit stresses and deformations within it. However, this type of increase in mass is usually incompatible with the required performances for the aircraft.
The purpose of the invention is a device designed to transmit approximately radial forces between a central region and end regions of the said device, the innovative design of which makes it capable of resisting very high bending forces with a significantly lower mass than a cylindrical pivot pin with a conventional design.
This result is achieved according to the invention using a device for transmission of forces in a direction approximately radial from a longitudinal axis of the said device, between a central region and two end regions of the device, the said device being characterized in that it comprises at least three ribs distributed around the said longitudinal axis and connected to each other in the said end regions, and at least one pair of elements in the shape of a star connecting the ribs together on each side of the said central region.
The ribbed structure of the force transmission device is capable of absorbing most bending forces due to the high moment of inertia that it creates for a given section. This design thus optimizes the mass of the structure.
It is particularly advantageous if the force transmission device according to the invention is made in a single part.
In one preferred embodiment of the invention, the ribs are uniformly distributed around the longitudinal axis of the said device.
In the same embodiment, the force transmission device is symmetric about a median plane perpendicular to the longitudinal axis of the said device.
All ribs can be made identical to simplify manufacture.
Advantageously, the ribs are connected to each other in the said end regions by two first rings and each of the star shaped elements comprises a second ring at its center, the first and second rings being along the said longitudinal axis.
Another purpose of the invention is a force transmission mechanism comprising a force transmission device as described above and a cylindrical rod acting as a pivot pin passing through the first and second rings so that it is fixed in bending to the force transmission device, the cylindrical rod acting as a bearing for a first part between a pair of star shaped elements adjacent to the central region and a second part beyond the first rings.
Advantageously, the elements forming bearings are then inserted between the cylindrical rod and each of the first and second rings.
Beyond the first rings, the cylindrical rod advantageously passes through two approximately plane webs, that can be fixed to the second part. The two webs thus form a double eye plate articulated onto a single eye plate connected to the first part, through the cylindrical rod, and two single eye plates articulated on two double eye plates linked to a fixed external structure through a second cylindrical rod acting as a pivot pin centered on an axis of rotation of the second part with respect to the fixed structure, this axis of rotation being parallel to the longitudinal axis of the force transmission device.
In one preferred application of the invention, the first part is a rod of an actuator with linear control supported by the fixed structure and the second part is an aircraft control surface.